Which is simply not true. Halflings were the most popular choice in our group, up until they were recently overtaken by warforged. Gnomes, Halflings and warforged are far more popular than humans, dwarves and elves. Now, my group is clearly not representative, but as the statistics show, some people like and choose to play gnomes and halflings.
It wouldn't help, because people do not choose their species based on what they encounter in adventures. And more importantly they don't need help. It doesn't matter if X is less popular than Y, or if Z never appears in some games (I've never seen a dragonborn PC in any of my games). They are there for the people who want to use them, and can be ignored by those who don't, without hurting anyone.